This invention relates to a process and an apparatus for coating a workpiece with a ceramic material and more particularly, to a process and an apparatus for coating a workpiece such as a machine component with a ceramic material using an energy beam such as an industrial laser, a CO.sub.2 laser or an electron beam as a heat source.
It is well known to form a coating of a ceramic material such as alumina, silicon nitride, and the like on a surface of a workpiece such as a machine component including a gear, a shaft, or a measuring sensor. By the use of this ceramic coating, many characteristics such as heat resistance, corrosion resistance, resistance to wear, and the like can be improved.
FIG. 1 is a schematic view showing a conventional apparatus for ceramic coating using a laser which is disclosed, for example, in Japanese Laid-Open 59-116373. In FIG. 1, a workpiece such as a substrate 1 and a ceramic material 2 are supported in a vacuum chamber 3, with a predetermined distance between the substrate 1 and the ceramic material 2. The vacuum chamber 3 is maintained at about 10.sup.-4 torr. A laser oscillator 4 such as a CO.sub.2 laser oscillator is disposed near the vacuum chamber 3 and generates a laser beam 5. The laser beam 5 generated is guided to a condenser lens 6 using mirrors 7, 8, and 9, where the laser beam 5 is appropriately condensed. Then, the condensed laser beam 5 irradiates the ceramic material 2 supported in a vacuum chamber 3 through a window 10. When the irradiated surface of the ceramic material 2 is heated by the laser beam 5 to reach the evaporation temperature of the ceramic material 2, a part of the ceramic material 2 evaporates to form particulates 11 thereof. The particulates 11 formed are then deposited on a substrate 1 to form a very thin coating of the ceramic material 2 thereon. Heaters 12 and 13 are also installed in the vacuum chamber 3 in order to increase the adhesion strength of the deposited coating of the ceramic material 2 and to stabilize the deposition condition thereof.
When desired, a plurality of coatings of the ceramic materials can also be formed on a single substrate one upon another. In this case, a plurality of ceramic materials and a plurality of heaters are provided in the vacuum chamber and the laser beam is irradiated in turn on the ceramic materials to form a plurality of coating layers of the ceramic materials on the substrate.
In the conventional process for coating a workpiece with a ceramic material, particularly, with a plurality of coatings of ceramic materials, the ceramic materials to be irradiated by a laser beam are provided in the shape of disks or cylinders, and the surface of the ceramic material is consumed as the evaporation progresses so that the position on the ceramic material at which the material is irradiated by the laser beam is altered momentarily, making it difficult to maintain evaporation conditions stable during the operation. Therefore, the thickness of the coating layer is not uniform or large particles of the ceramic material are scattered from the ceramic material 2, and a stable coating cannot be achieved. In addition, due to the requirement for the heating sources such as heaters for each ceramic material, the structure and the operation of the coating apparatus is complicated and a large operating space for coating is needed.